During the rolling of metal strips, in particular during cold rolling, the tensile stress distribution in the metal strip, along the metal width, has to be determined on line i.e., it usually has to be measured, since the tensile stress distribution is the decisive variable for controlling the flatness of the metal strip.
For example, metal metal strip is guided over a measuring roll, i.e., a segmented guide roll, which has piezoelectric pressure sensors at intervals of about 2-5 cm. The force acting on the sensors in this case is a measure of the tensile stress distress distribution. The method involves contract--and can therefore leave behind impressions in the metal and, in addition, involves wear and is thus maintenance intensive.
Furthermore, German Patent No. 26 17 958 describes a device for measuring the tensile stress of a metal strip, oscillatory waves being generated in the metal strip using electric hammers, and their propagation being measured. This method is also subject to the disadvantages mentioned above.
Furthermore, German Patent No. 31 30 572 describes the operation of measuring the tensile stress of a metal strip using ultrasound. To this end, the metal strip is made to oscillate using ultrasound, and the propagation of this oscillation is measured. However, it has been shown that this method is suitable only in exceptional cases, in particular in the case of particularly thin metal strips, because of the low energy transmission when ultrasound is used.
U.S. Pat. No. 3,538,756 descries a system in which a constant stream of air is blown against the metal strip in order to push the latter away for the purpose of achieving a deflection of the metal strip.